Polyploidy breaks speciation barriers in Australian burrowing frogs Neobatrachus

Abstract

Polyploidy has played an important role in evolution across the tree of life but it is still unclear how polyploid lineages may persist after their initial formation. While both common and wellstudied in plants, polyploidy is rare in animals and generally less understood. The Australian burrowing frog genus Neobatrachus is comprised of six diploid and three polyploid species and offers a powerful animal polyploid model system. We generated exome-capture sequence data from 87 individuals representing all nine species of Neobatrachus to investigate species-level relationships, the origin and inheritance mode of polyploid species, and the population genomic effects of polyploidy on genus-wide demography. We describe rapid speciation of diploid Neobatrachus species and show that the three independently originated polyploid species have tetrasomic or mixed inheritance. We document higher genetic diversity in tetraploids, resulting from widespread gene flow between the tetraploids, asymmetric inter-ploidy gene flow directed from sympatric diploids to tetraploids, and isolation of diploid species from each other. We also constructed models of ecologically suitable areas for each species to investigate the impact of climate on differing ploidy levels. These models suggest substantial change in suitable areas compared to past climate, which correspond to population genomic estimates of demographic histories. We propose that Neobatrachus diploids may be suffering the early genomic impacts of climate-induced habitat loss, while tetraploids appear to be avoiding this fate, possibly due to widespread gene flow. Finally, we demonstrate that Neobatrachus is an attractive model to study the effects of ploidy on the evolution of adaptation in animals.

Low dispersal and ploidy differences in a grass maintain photosynthetic diversity despite gene flow and habitat overlap

“…Previous genomic analyses found evidence of admixture between C 4 and non-C 4 plants in the Central Zambezian region (Bianconi et al, 2020;Olofsson et al, 2016), and the recurrent mixing of the genetic groups corresponding to the two photosynthetic types is confirmed here with our denser sampling. Strong admixture was detected in particular in polyploid individuals (Figure 4; Figure S7), mirroring other study systems (Fay et al, 2019;Grabowski et al, 2014;Novikova et al, 2020;Parisod et al, 2010;Schmickl & Koch, 2011).…”

Evolution of gene-rich germline restricted chromosomes in black-winged fungus gnats through introgression (Diptera: Sciaridae)

“…Although animals of similar divergence have been successfully hybridised in the lab [47], we present the first evidence for a cross-family hybridisation event in nature with evolutionary consequences. Gene flow between very divergent lineages seems to be frequently associated with polyploidisation (for example in burrowing frogs [48], or Arabidopsis [49]), supporting our view that GRCs evolved in the current form a whole genome introgressed from the ancestor of Cecidomyiidae.…”

Adaptive introgression: how polyploidy reshapes gene flow landscapes

“…In cases of secondary contact between cytotypes (incomplete isolation), hybridisation may then allow transfer of traits with adaptive benefits. Such adaptive gene flow can occur between different ploidies (overwhelmingly from diploid to tetraploid, via unreduced gametes) within a single species (Baduel et al, 2018;Monnahan et al, 2019), or among close relatives (Schmickl & Koch, 2011;Marburger et al, 2019;Novikova et al, 2020), often in a cytotype-specific manner. Stebbins (1956) was the first to outline WGD-mediated gene flow within the polyploid complex Dactylis glomerata, based on cytotaxonomics.…”

“…While there is highly provocative parallel evidence in a diploid/ polyploid frog system (Novikova et al, 2020), the most detailed…”